TABLE OF CONTENTS

INTRODUCTION........................................................................................................................

OBJECTIVES...............................................................................................................................

THEORY......................................................................................................................................

APPARATUS...............................................................................................................................

PROCEDURES.............................................................................................................................

DATA AND RESULTS...............................................................................................................

DISCUSSIONS.............................................................................................................................

CONCLUSIONS...........................................................................................................................

REFFERENCES...........................................................................................................................

1

INTRODUCTION

Figures 1, 2 and 3 show the rotor and nozzle arrangements for the axial flow impulse turbine

(FM3O), the radial flow reaction turbine (FM31) and the Pelton turbine (FM32).

In an impulse turbine (Figure 1) the kinetic energy of a jet leaving a high pressure

stationary nozzle is converted on impact with the turbine blades to rotational mechanical

energy. As the water exiting the jet is at atmospheric pressure, the force exerted on the rotor is

entirely due to changes in the direction of the flow of water. The impulse turbine is therefore

associated with considerable changes of kinetic energy but little change in pressure energy. In

the case of the FM3O four independently controlled nozzles are installed around the rotor.

In a reaction turbine (Figure 2) the water is subject to a pressure drop as it flows

through the rotor. The reaction turbine is therefore associated with considerable changes in

2

Figure 1 : Rotor and nozzle arrangement of the impulse turbine

Figure 2 : Rotor and nozzle arrangement of the reaction turbine

Figure 3 : Rotor and nozzle arrangement of the Pelton turbine

pressure energy but little change in kinetic energy and is sometimes called a pressure turbine.

In the case of the FM31 water enters the rotor via a face seal and is discharged tangentially

through two nozzles at the periphery of the rotor. The nozzles therefore move with the rotor.

The Pelton turbine (Figure 3) is the most visually obvious example of an impulse

machine. A spear valve directs a jet of water at a series of buckets which are mounted on the

periphery of a rotor. As the water exiting the spear valve is at atmospheric pressure, the force

exerted on the rotor is entirely due to changes in the direction of the flow of water. The Pelton

turbine is therefore associated with considerable changes of kinetic energy but little change in

pressure energy.

The spear valve allows the jet diameter to be varied which allows the water flow rate

to be varied with a constant jet velocity. Large turbines may include more than one spear

valve around the periphery of the rotor. In the case of the FM32 a single spear valve is

installed.

The operating characteristics of a turbine are often conveniently shown by plotting

torque T, brake power Pb, and turbine efficiency Et against turbine rotational speed n for a

series of volume flow rates Qv, as shown in Figure 4. It is important to note that the efficiency

reaches a maximum and then falls, whilst the torque falls constantly and linearly. In most

cases a turbine is used to drive a generator in the production of electricity. The speed of the

generator is fixed to produce a given frequency of electricity. The optimum conditions for

operation occur when the maximum turbine efficiency coincides with the rotational speed of

the generator. As the load on the generator increases then the flow of water to the turbine

must increase to maintain the required operating speed.

This Armfield Capture unit is designed to allow students to determine the operating

characteristics of either an Axial Flow Turbine (FM3O), a Radial Flow Reaction Turbine

(FM31), or a Pelton Turbine (FM32), rapidly and meaningfully, using ‘on-line’ data

3

Figure 4 : Example characteristics of a turbine at different flow rates

acquisition and analysis. Test results may be displayed in tabular and graphical forms, and it

is a simple matter to repeat or add to the data to cover areas of the turbine performance of

particular interest.

OBJECTIVES

i. To observe and understand the operating characteristics of the turbines.

ii. To study the basic concept of impulse turbine.

iii. To relate the actual situation to the theoritical statement.

THEORY

Turbines are classified in two general categories : impulse and reaction. In both types the fluid

passes through a runner having blades. The momentum of the fluid in the tangential direction

is changed and so a tangential force on the runner is produced. The runner therefore rotates

and performs useful work, while the fluid leaves it with reduced energy. The important

feature of the impulse machine is taht there is no change in static pressure across the runner.

In the reaction machine, the static pressuredecreases as the fluid passes through runner.

For any turbine, the energy held by the fluid is initially in the form of pressure, ie. a

high level reservoir in a hydro-electric scheme.

The impulse turbine has one or more fixed nozzles, in each of which this pressure is

converted to the kinetic energy of an unconfirmed jet. The jet of fluid then impinge on the

moving blades of the runner where they lose practically all their kinetic energy.

In a reaction machine, the changes from pressure to kinetic energy take place

gradually as the fluid moves through the runner, and for this gradual changes of pressure to be

possible the runners must be complete enclosed and the passages in it entirely full of the

working fluid.

4

The general relationship between the various forms of energy, based on the 1st Law of

Thermodynamics applied to a unit mass of fluid flowing through a ‘control volume’ is

expressed as :-

−W S=d ( v2/2 )+g .dz+∫ vol .dp+F

Where :

-Ws is the work performed by the fluid on the turbine

d(v2/2) is the change in kinetic energy of the fluid

g.dz is the change in potential energy of the fluid

∫ vol . dp is the change in pressure energy,where ‘vol’ is the volume per unit mass of the

fluid. For an incompressible fluid of constant density Rho, this term is equal to

∫ dp/ R ho or (p1-p2)/Rho where p2 refers to the turbine discharge outlet and

p1 to the turbine inlet

F is the frictional energy loss as heat to the surroundings or in heating the fluid

itself as it travels from inlet to outlet

The first three terms of the right hand side represent the useful work Wa ie.

−W a=( v12−v2

2

2 )+g ( z1−z2 )+(p1−p2

R ho)

Where subscript 2 refer to the turbine outlet and subscript to the inlet.

The term Wa represents the actual work produced in changing the energy stages of a unit mass

of

fluid. This may alternatively be presented as the total dynamic head H of the turbine, by

converting

the units from work per unit mass to head expressed as a length :-

H=( v12−v2

2

2 g )+( z1−z2 )+(p1−p2

R h o . g)

5

It can be assumed for the purposed of the following practical experiments that the fluid is

incompressible (i.e. is constant)

The variable obtained from the sensors on the equipment are :-

Symbol Term Units

dPo Orifice differential pressure Pa

P1 Turbine inlet pressure Pa

n Rotational speed of the pump Hz

Fb Brake force on turbine N

Constant used in the calculation are :-

Symbol Term Value Units

d Orifice diameter 0.009 m

Cd Discharge coefficient 0.63

r Pulley radius 0.024 m

Water density 998.2 kg/m3

Calculated variables are :-

Symbol Term Units

Qv Volume flowrate m3/s

Hi Input head to turbine m

Ph Hydraulic power available to turbine W

T Torque Nm

Pb Brake power W

Et Overall efficiency %

6

Formula used are :-

Qv=Cd . . d2 .√2 . p . dPo

4 p

H i=P 1g

Ph=g H i .Q v

T=Fb. r

Pb=2n . T

Et=Pb

Pe

×100

APPARATUS

7

Figure 5 : Turbine Service Unit Figure 6 : Armfield Controller

The unit consists of a clear acrylic reservoir (1), a circulating pump and associated pipe work

installed on a support plinth, which is bench mounted. The reservoir incorporates a drain

valve (2) at the base and a flange (3) at the top, to which the appropriate turbine is attached.

Water circulation is provided by a single stage centrifugal pump (5) driven by an

integral electric motor (4). The motor requires a single phase electricity supply.

The pump discharge pipe corporate a screwed connector which mates with the inlet pipe on

the appropriate turbine.

8

3

1

2

4

5

Figure 7 : Integrating Wattmeter Figure 8 : PC Turbine Domenstration Unit

The flow of water is measured using a differential pressure sensor SPW1 which is

connected across an orifice plate at the entrance to the pump inlet pipe. The pressure sensor is

connected between the tapping on the orifice plate and a tapping in the wall of the reservoir.

Additional tapping’s are provided for the connection of the appropriate instrumentation (not

supplied) to facilitate calibration of the differential pressure sensor.

The differential pressure sensor is connected to channel 1 on the IFD interface

console.

PROCEDURES

The laboratory equipment was set up by the lab session facilitator as follows.

a) The Turbine Service Unit FM3SU was placed in a suitable location adjacent to a

compatible microcomputer.

b) The drain valve (2) at the base of the reservoir was ensured is fully closed.

c) The Differential Pressure Sensor SPW1 (9) is checked so it is connected to the two

tappings at the front of the reservoir. P1 LOW on SPW1 must be connected to the

tapping on the orifice plate and HIGH P2 must be connected to the tapping in the wall

of the reservoir.

d) The reservoir (3) was filled with clean water until the level is approximately 100mm

below the top.

e) The flexible tubing connecting differential pressure sensor SPW1 to the orifice plate

should be primed with water using the priming syringe supplied.

f) The syringe was filled with clean water. Each flexible tube was disconnected from the

tapping on the reservoir.

g) The syringe and back-fill the flexible tube were inserted with water. When all air

bubbles have been expelled the tubing was reconnected to the reservoir.

h) The required turbine (FM3O FM31 or FM32) was placed on top of the reservoir,

ensuring that the O-ring seal is located in the recess in the top flange of the reservoir.

Loosely attach the pipe connector from the service unit to the turbine, then, the base

plate of the turbine was fastened to the top flange of the reservoir by tightening the

thumb screws. Finally tighten the pipe connector.

i) The interface console IFD was placed alongside the computer.

9

j) The mains supply lead from an appropriate electrical supply was connected to the

MAINS INPUT socket on lED ensuring that the electrical supply is compatible with

the console (indicated on the rear of the console).

k) Water was checked either it circulates through the turbine. The pump was then turned

off.

l) Each of the sensor conditioning boxes was connected to the appropriate SENSOR

SOCKETS on the front of IFD, using the numbered connecting leads, as follows:

Channel 1 to sensor SPWI on the Turbine Service Unit (FM3SU)

Channel 2 to sensor SPH2 on the base plate of the appropriate Turbine

Channel 3 to sensor SSO2 on the base plate of the appropriate Turbine

Channel 4 to sensor SLRI on the base plate of the appropriate Turbine

Brake Belt Removal And Refitting

The position of the slave pulley was adjusted by sliding the slave pulley bracket (3)

back and forth, so that the bracket is upright when the belt is lightly tensioned between the

turbine pulley and slave pulley.

As equipment was fully set up, the student was needed to carry out these following

procedures:

a) The brake force at the software interface was adjusted, starting from initial value of

zero.

b) The stable reading was then recorded by pressing the ‘record’ function from the

software. The data then shows up at the table of data which is automatically generated

by the software.

c) The brake force is then adjusted by a small increment of 0.1 to 0.9 N up to total of 5 N

brake force. Thus, this process was repeated by simply repetition of steps 1 and 2.

d) The collected data is then used for the software to generate graphs as the result. This is

again automatically generated by using the software.

10

DATA AND RESULTS

11

Sample calculation:

Sample data from Sample number 8 from the table

g=9.81m/ s2

d=0.009 m

C d=0.63

ρ=998.2kg

m2 d Po=26.284 kPa

Volume flow rate, Qv,

Qv=Cd π d2√2 ρ d Po

4 ρ¿ 0.63 × π× 0.0092 ×√2× 998.2 ×26.284 k

4 (998.2 ) ¿0 .291 dm3/ s

Impact head, Hi,

H i=P1

ρg¿ 248.828 k

998.2× 9.81¿25 . 41 m

Hydraulic Input Power,Ph,

Ph= ρgQ v H 1¿998.2 ×9.81 × 0.291× 10−3 ×25.41¿72 . 41W

Torque,T

12

T=Fbr¿1.9 ×0.024¿0 .0456 Nm

Brake power,Pb

Pb=2πnT¿2 ×227

×76 × 0.0456¿22 W

Turbine efficiencies,

Egr=Pb

Ph

×100 %¿ 2272.41

×100 %¿30 . 5 %

DISCUSSION

13

CONCLUSION

14